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Tank Stiffener Rivets Not Flush to Skin

J

jpharrell

Well Known Member
I riveted my first set of stiffeners to tank skin last night with tank sealant. I used tank dimple dies on the skin and ribs, applied a tiny dab of sealant to the dimples, inserted the rivets and back riveted them as recommended in the instructions. After removing excess sealant I found that virtually all the rivet manufactured heads protrude about 0.010 inch above the surface of the skin. Did anyone else have this problem? I checked them before applying sealant with a dry rivet and they were flush. I'm trying to decide whether to drill them out or just build on. My empennage skin rivets are all nice and flush. You can hardly feel them if your run your hand across the surface but these are clearly proud of the skin surface.

John H.
RV7A building wings
www.johnsrv7a.wordpress.com
 
hmm, just got done with mine...no problems like that. Might be a silly question, but are you sure you actually have tank dimple dies? Mine (from Avery) are labeled as such, not sure if all of them are?


jpharrell said:
I riveted my first set of stiffeners to tank skin last night with tank sealant. I used tank dimple dies on the skin and ribs, applied a tiny dab of sealant to the dimples, inserted the rivets and back riveted them as recommended in the instructions. After removing excess sealant I found that virtually all the rivet manufactured heads protrude about 0.010 inch above the surface of the skin. Did anyone else have this problem? I checked them before applying sealant with a dry rivet and they were flush. I'm trying to decide whether to drill them out or just build on. My empennage skin rivets are all nice and flush. You can hardly feel them if your run your hand across the surface but these are clearly proud of the skin surface.

John H.
RV7A building wings
www.johnsrv7a.wordpress.com
Click to expand...
 
Recently finished mine. I did drill out a couple of the first tank stiffener rivets as I wasn't pushing down hard enough with the back rivet set.

The ones that are a problem are the tank skin to baffle rivets where you countersink the skin instead of dimpling. I practiced on scrap until I could countersink as deep as possible without creating a knife edge but the rivets are still a hair (technical measurement) proud. I'll live with them as the tanks are leak free.
 
I'm sure they are tank dimple dies. I ordered them from Cleveland Tools, they have a T marked on the part and the cone is slightly larger than my standard dimple dies. One thing I did not do was clean off the excess sealant squeezed out when I put the rivets in before applying rivet tape. I'm wondering if that might have been part of the problem.
 
My first thought is to check how much proseal you're putting in the rivet hole. Sounds like way too much. If I were you, I'd clean the excess off like you said, and see if that helps. I think you're on to something there.

Beyond that, if you checked the rivets and dimples for correct fit beforehand and all is well, I'm wondering if your backriveting set needs a stiffer spring. I'm just thinking, a stiffer spring would push the parts down harder against the backriveting plate, wouldn't it? I'm just theorizing here, but you have to wonder why this happened if everything fit right beforehand.

Another idea I'm wondering about is to wait a moment after pushing the backriveting set down before pulling the trigger. This technique might allow the proseal a moment to ooze out of the rivet hole and the rivet to seat itself properly in the dimple before the rivet gun goes off.

I'm also wondering what you're using for rivet tape, and if it might be part of the problem. You might try some rivets without the tape.

It would be easy enough to try these ideas on some scrap to check. Let us know what you find out, okay?
 
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Good suggestions Bruce. The amount of sealant around the dimples is very small but maybe enough to keep the skin slightly off the back rivet plate around the rivet head because the goop is thick and spreads slowly. Next time I'll clean off excess before applying rivet tape and I'll wait a few seconds after pressing down and before firing the trigger and see if that helps.
 
jpharrell said:
...... After removing excess sealant I found that virtually all the rivet manufactured heads protrude about 0.010 inch above the surface of the skin. Did anyone else have this problem?.....
Click to expand...
John,

The condition you describe is very common. Having never used tank dimple dies myself, I found that dozens of fuel tank rivets tended to sit a bit proud. It is merely a cosmetic issue. Still, I like to think of myself as having an eye for cosmetics and the condition was very easily resolved by putting a high speed rivet shaver to work on the offending rivets. The result are perfectly flush rivets. See if you can borrow a "real" rivet shaver from someone, perhaps a local EAA chapter.

290t005.jpg
 
BSwayze said:
My first thought is to check how much proseal you're putting in the rivet hole. Sounds like way too much. If I were you, I'd clean the excess off like you said, and see if that helps. I think you're on to something there.

Beyond that, if you checked the rivets and dimples for correct fit beforehand and all is well, I'm wondering if your backriveting set needs a stiffer spring. I'm just thinking, a stiffer spring would push the parts down harder against the backriveting plate, wouldn't it? I'm just theorizing here, but you have to wonder why this happened if everything fit right beforehand.

Another idea I'm wondering about is to wait a moment after pushing the backriveting set down before pulling the trigger. This technique might allow the proseal a moment to ooze out of the rivet hole and the rivet to seat itself properly in the dimple before the rivet gun goes off.

I'm also wondering what you're using for rivet tape, and if it might be part of the problem. You might try some rivets without the tape.

It would be easy enough to try these ideas on some scrap to check. Let us know what you find out, okay?
Click to expand...

I had similar problems using my back rivet set and don't use it any longer.
 
Rick6a said:
John,

The condition you describe is very common. Having never used tank dimple dies myself, I found that dozens of fuel tank rivets tended to sit a bit proud. It is merely a cosmetic issue. Still, I like to think of myself as having an eye for cosmetics and the condition was very easily resolved by putting a high speed rivet shaver to work on the offending rivets. The result are perfectly flush rivets. See if you can borrow a "real" rivet shaver from someone, perhaps a local EAA chapter.

290t005.jpg
Click to expand...

i would love to borrow one of these........anyone reading this have one?!
 
I had a similar problem with control surface stiffeners. I've found that moving my backrivet plate from the workbench to the concrete floor gives more consistent results. I hope I get this thing done before I'm too old to work on my knees.:rolleyes:
 
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